Method and apparatus for constructing a concrete structure



Jan. 14, 1964 H. HARRINGTON 3,118,010

METHOD AND APPARATUS FOR CONSTRUCTING A CONCRETE STRUCTURE Filed Oct.10, 1960 &

:IIIIII-IIIIII FIG? 4 INVENTOR. fforrall Harrz'ngi United States Patent0 3,118,919 METHOD AND APPARATUS FQR (IUNSTRUCTING A $NRETE STRUCTUREHer-rad Harrington, 822 61st St La Grange, lll., assignor of one'halr toEvan Hiznrnel Filed Get. 19, 19:58, Ser. No. 61,767 16 Claims. (1.264-32) This invention relates to a building structure and method ofmaking the same and, more particularly, to c. shell-form self-supportingconcrete structure fabricated within an inflatable form.

The method or" making shell-form concrete str rctures upon an inilatableform is known to the prior art. As previously practiced, a pneumaticform anchored to a foundation was inflated to shape and concrete sprayedthereon in thin layers. When the concrete had hardened sufiiciently, theform was deflated and removed leaving the hardened shell behind andconcrete was then added to form walls of desired thickness. See Nelipatent, No. 2,335,306.

This method of making such structures and the structures themselves haddisabling disadvantages. The concrete being required to be sprayed onthe outer surface of the form was adversely affected by the weather.Windy conditions would tend to distort the form before the concretecould set. Workrnen could not work under rainy or cold conditions andvariations in humidity and oerature would adversely affect the concreteand the of the hardened material.

in addition, the structure itself developed faults due to the weight ofthe concrete on the dome and the side wall portions crack and crumble atthe plane or" rupture.

A tempts have been made to eliminate the cracking by ssing the concreteout without success. The use of tensioning rings resulted in seriousdeformation of the side walls and ire-stressing the concrete wasconsidered impossible. As the prior art states: Due to the curveture ofthe form side wall, it was not considered ieasable or even possible toapply wire mesh reinforcement to the pneumatic form in such a mannerthat it could be pretensioned so as to place the hardened concretematerial of the structure wall under compression follow removal of theform.

Accordingly, it is an important object of the present inver n to providea method of building a shell-form concrete self supporting structurewhich is free from the 3 of the prior art, to provide a structure crackor crumble. -,ect of the invention is to provide a of building suchstructures wherein the concrete is from the inside of the form asopposed the outside application of 1' e prior art, thus eliminating or rducir the wea her 5 encountered by th prior art.

tent ect of the FY3551 the employment of a network of wire ropes on theinside of the form whi" sy be varied so that the snaps of rnay in tinbefashioned to accommodate a .y of the uses the finished strure.

-*n of greater ten e strength, greater dimenscnal s greater resistanceto puncture damage during construction, which has absorb or surface towhich the concrete is app-lied to aid said concrete.

r crtant object is to provide a form pressure greater than thatcorreweight of the wet concrete.

er object is to provide a structure v the concrete crumbling.

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The foregoing and other objects and advantages of the invention willbecome apparent from a consideration of the following specifications andthe accompanying drawings wherein:

PEG. 1 is a part sectional and part elevational view or" a shell-formstructure made in accordance with the present invention.

FIG. 2 is a top plan view of the structure shown in FIG. 1, partiahybroken away.

PEG. 3 is a sectional view taken on line 3-3 of FIG. 2.

FIG. 4 is a cross sectional view of a portion of the inflated formbefore concrete is applied.

PEG. 5 is a perspective view of a portion of the plastic outer layer ofthe inflatable form showing a closed air outlet slit.

Referring to the drawings, FIG. 1 discloses a concrete structureindicated generally by the reference numeral 1%, erected on a suitablefoundation of concrete or other like material. As shown, the structureis erected by applying a cementitious material on the inner surface ofan inflatable form of predetermined size and shape. Because thecernentitious material is sprayed on the inside surface, it is necessaryto ide a form oiunique construction whereby the wet cementitiousmaterial is caused to adhere strongly to downwardly sloping concavesurfaces.

The form provided comprises a laminated envelope 12 having inner textilelayer 14 and an outer impervious layer 15, preferably formed of plasticfilm although other appropriate materials may be used. As may be seen inFIGS. 4 and 5, the outer layer is is provided with a plurality of slitsor bleeding apertures 21 for reasons here inafter described. The innerand outer layers of the envelope 1?. are secure to ether atpredetermined intervals by means of uitable connectors 18 and aplurality of hooss Zll depentnng inside the envelope 12 are attachedthereto. The hooks 2d are adapted to hold a network or system of wireropes 22 which assume their final position on the inside of the envelopewhen said envelope is inilated.

The ropes 22 have a plurality of functions. They reintorce the envelope22 against internal air pressure of inflation thereby preventingblowouts and permitting the envelope o be made of thinner and lessexpensive material than would otherwise be possible. Being under innaton pressure, the wire ropes 22 are subjected to conab tensile stressduring the placement of the con 3 case of the pressure after theconcrete has een applied has hardened subjects the concrete shellocornpressive stress in both ions as the wire rope tend to contract.Thus a restressing is achieved win-o eliminates or greatly redu es theprobability of subsequent or ring of h shell due to thermal stresses,wind or shrinkage. Furthermore, the placement of the ropes 22 may bevaried in a manner to cause the envelope 12 to tule on a variety offorms and shapes to suit any particular need so that a standard formenvelope be to form differently oerl structures.

nliated fi xible forin tends to assume shapes whose s are circle arcsreflected the fact that a circle is In the embodiment shown in thedrawing, e pc is designed so that ends 24 are quarter so ere-s and theinterm te portions 2 6- form a series oi" CGHE'IGmt Q s mentseach havingthe form or a See FEGS. 1 and 2. Such arrangement is c able because ittakes advantage of the natural form time ted envelope and the s"- uepermits a mi tea to enclose a rnt'riniu floor area, thereby decreasingbuilding costs. *therniore, the segor bellows-like shape allows thebuilding to ex- 3 pand thermally without requiring the use of expensiveexpansion joints. The finished shell will be structurally stable withrelatively few bending moments regardless of its size.

Giving attention now to the method of constructing the building shell, asuitable foundation 28 is first laid. In large structures, thefoundation walls may be of a size to permit doors 29 to be formedtherein. The envelope 12 with the wire ropes 22 attached to its innersurface is arranged on the foundation 2% and the lower edge 39 of theenvelope is then secured thereto. Compressed air is introduced to theinterior of the envelope to inflate it to its predetermined form. Theenvelope then is ready for processing.

Because the novel method requires that the application of thecementitious material be applied on the inside of the envelope 12, it isnecessary that the work be done under inflation pressure. It has beenfound that inflation pressure in the range of 25 to 50 pounds per squarefoot produces satisfactory results. Physiologicallly, such a pressurepresents no hazard to the workman since it is a variation in absolutepressure of only 2 to 3% from normal atmospheric pressure. Workrnenenter the interior of the inflated form through a suitable entranceprovided for that purpose, where they are protected from the weather.The inner surface of the envelope 12 is then sprayed with a lightweightcementitious material 32, preferably one with the expanded shaleaggregate because of its low creep properties, and continues until thewire ropes 2,2 are fully embedded in the cementitious material 32, asseen in FIG. 3.

The inflation of the envelope 12 is maintained during application andhardening of the cementitious material. The inflation pressure withinthe range above stated will always be greater than that corresponding tothe weight of the wet cementitious material per square foot. For examle, a lightweight cement weighing 80 pounds per cubic foot will weighapproximately pounds per square foot in a 3-inch thickness. Thus, theinflation pressure within the stated range will always provide a safetyfactor for sustaining the wet material as well as assuring stability ofthe envelope aginst the effects of wind and preserving the desired shapeof the building as the concrete hardens.

The adherence of the wet cementitious material 32 to the downwardlysloping concave surfaces of the envelope 12 is also aided by thecontrolled flow of air through the envelope. As shown in the illustratedembodiment as the envelope 12 becomes inflated, air flows through theinner textile layer 14 and pufls the outer layer 16 causing the normallyclosed edges of slits 21 in the plastic layer to separate permitting airto escape, as is shown in FIG. 4. This flow of air pulls a quantity ofthe wet cementitious material 32 into the interstices of the textilelayer 14 causing the material to strongly adhere to the wall surfaces.The number and size of the slits 21 are predetermined to preciselyregulate the air flow through envelope 12 and in that respect the slitsperform the function of air valves.

It must then be seen that the flow of air through the envelope '12 is animportant step in the process and that in the embodiment shown, such airflow is controlled by the structure of the plastic 16 having the slitsor bleeding :apertures 21. It has been found that the air flow may alsobe controlled by controlling the porosity of the textile ma erial, inwhich case the plastic outer layer 16 may be dispensed with. In such astructure, the air pressure required for a desired form is calculatedand the textile material is treated by applying a solution containing apolyvinyl chloride or other similar solution thereto, thereby fixing theporosity of the material within prescribed limits. in such a structure,when the air pressure within the inflated envelope reaches apredetermined range, air will bleed through the interstices of thematerial just as it 'Will bleed through the slits 21 in the embodimentshown. The nature of the solution used in treating the textile materialland its application thereto are well known to workers in this art, andof themselves do not form a part of the present invention.

The control of air flow through the envelope 12 is particularlyimportant when constructing large concrete shells because the envelopemust be correspondingly larger. For example, it is contemplated that theshell shown in FIGS. 1 and 2 of the drawings is to be 400 feet long, 200feet wide and 60 feet high. Without any air flow, as would be the casewith an impervious plastic sheet, the cement would have difficultyadhering to the inner surfaces of the form. If the air flow is notcontrolled, difliculty would be encountered in inflating the envelopewithout the use of expensive machines which would make the processuneconomical. However, by controlling the air flow, as above described,and keeping it within tolerable and predetermined limits, even verylarge envelopes may be inflated by machinery which is economical andreadily available.

After the cement hardens, the pressure is released and the buildingretains its shape because of the structural strength of the cementitiousmaterial 32, reinforced by the wire ropes 22. Upon the release ofpressure, the outer plastic layer 16 moves from its putfed position,shown in dotted line in FIG. 3, to a collapsed solid line positionsubstantially coextensive with the inner textile layer 14. The edges ofthe slits 21 in the plastic layer 16 then move back together to preventthe entrance of moisture.

As previously stated, the wire ropes 22 are subjected to considerabletensile stress by the inflation of the envelope 22. Upon release of thepressure after the concrete has hardened, these ropes tend to contractsubjecting the hardened concrete shell to compressive forces whichgreatly reinforce and strengthen it. It is apparent that to furthersupport the shell, particularly in large structures, suitable supportingcolumns (not shown) may be provided in a manner well known in the art.

It is to be noted that the envelope 12 remains a permanent part of theconcrete shell 10 and serves as a waterproof exterior cover therefor.Consequently, there is no need for a separately applied expensivewaterproof cover or waterproof coating for the shell.

Thus, it will be understood that the present invention comprehends anovel method of constructing a concrete shell upon a novel inflated formwherein concrete is applied upon the inside of the form and whose shapemay be varied and tensile strength increased by a system of wire ropesembedded in the concrete. This produces a novel structure wherein thehardened concrete is prestressed to prevent cracking or crumbling.

While the present invention has been explained and described withreference to specific embodiment of method and structure, it will beunderstood nevertheless that numerous modifications and variations aresusceptible of being incorporated without departure from the essentialspirit or scope thereof. Accordingly, it is not intended for anunderstanding of this invention to be limited by the foregoingdescription nor by the illustrations in the annexed drawings, except asindicated in the hereinafter appended claims.

What is claimed as new and desired to be secured by Letters Patent ofthe United States is as follows:

1. The method of constructing concrete shell structures, of a shapewhose elements are circle arcs, by use of an inflated pneumatic formconforming essentially to the ultimate extensive configuration of thestructure, comprising the steps of providing a laminated inflatablemember having an inner layer capable of receiving and retaining wetcementitious material, lining said inflatable member with a network ofwire ropes in predetermineddesign, securing said lined member to asuitable foundation, inflating said member with a pressure greater thanthe corresponding weight of wet cementitious material to be appliedthereto and thereby stressing said wire ropes, applying wet cementitiousmaterial to the inner surface of said member and to the said wire ropes,and maintaining said inflation pressure while the said cementitiousmaterial hardens whereby the stressed wire ropes are embedded in saidmaterial and the hardened material is compressed when inflation pressureis released.

2. A method as in claim 1, wherein the inner layer is a textilematerial.

3. A method as in claim 2, wherein the outer layer is a plastic filmbonded to the inner layer at predetermined intervals and havingvalve-like slits therein to permit air bleeding and pressure control.

4. A method as in claim 3, wherein the inflation pressure is within therange of to 50 pounds per square foot.

5. The method of constructing concrete shell structures of a shape whoseelements are circle arcs by use of an inflated pneumatic form conformingessentially to the ultimate extreme configuration of the structurecomprising the steps of securing a laminated inflatable member to asuitable foundation, said member having an inner layer of textilematerial capable of receiving and retaining wet cementitious material,and an outer layer of plastic film bonded at predetermined intervals tosaid inner layer and having valve-like slits therein for pressurecontrol, inflating said member to a pressure within the range of 25 to50 pounds per square foot, applying wet cementitious material to theinner layer of said member and maintaining said inflation pressure untilthe cementitious material hardens.

6. The method of constructing concrete shell structures of a shape whoseelements are circle arcs by use of an inflated pneumatic form conformingessentially to the ultimate extreme configuration of the structure,comprising the steps of providing an inflatable member of textile fabricwhich has been treated to eflect a desired degree of porosity to controlthe flow of air therethrough and whose surface is capable of receivingand retaining wet cementitious material, lining said member .with anetwork of wire ropes in predetermined design, securing said linedmember to a suitable foundation, inflating said member with a pressuregreater than the corresponding weight of wet cementitious material to beapplied thereto and thereby stressing said wire ropes, applying saidcementitious material to the inside surface of said member and to saidwire ropes, thereby embedding said wire ropes in said material andmaintaining said inflation pressure while the wet cementitious materialhardens to maintain the stressed wire ropes embedded in said material,whereby the hard ened material is compressed when inflation pressure isremoved.

7. A method as in claim 6 wherein the inflation pressure during theapplication of the wet cementitious ma 6 terial is maintained within therange of 25 to pounds per square foot.

8. An inflatable form for making concrete shell structures comprising aflexible envelope of such size and shape that upon inflation it assumesthe size and shape of the finished concrete shell structure, saidflexible envelope comprising a porous inner textile layer and an outerairimpervious layer of plastic film, said plastic layer being bonded tosaid textile layer at predetermined intervals, and a plurality of slitsformed in said plastic film so that when the flexible form is inflatedthe slits function as valve-like members and part far enough to permit acontrolled fiow of air through the flexible form.

9. An inflatable form for making concrete shell structures comprising aflexible envelope of such size and shape that upon inflation it assumesthe shape of the finished concrete shell structure, said flexibleenvelope comprising a porous inner textile layer and an outer layer ofplastic airtight film, said plastic film being attached to said textilelayer at predetermined intervals, a plurality of slits formed in saidplastic film so that when the flexible envelope is inflated, the slitsfunction as valve-like members and part far enough to permit acontrolled flow of air through the envelope, and a plurality of wireropes attached to the inside of said flexible envelope at predeterminedintervals before the envelope is inflated, said ropes being adapted tocontrol the shape of the inflated envelope and to reinforce the concreteapplied to said form.

1 0. An inflated form for making concrete shell structures comprising -aflexible envelope of such size and shape that upon inflation it assumesthe size and shape of the finished concrete shell structure, saidenvelope comprising a textile material Whose surface has been treated toeflect a desired degree of porosity to control the flow of airtherethrough, and a network of wire ropes of predetermined designattached to the inside of said envelope at predetermined intervalsbefore the envelope is inflated, said wire ropes being adapted tocontrol the shape of the inflated envelope and to reinforce andprestress the concrete applied to said form.

References Cited in the file of this patent UNITED STATES PATENTS

1. THE METHOD OF CONSTRUCTING CONCRETE SHELL STRUCTURES, OF A SHAPEWHOSE ELEMENTS ARE CIRCLE ARCS, BY USE OF AN INFLATED PNEUMATIC FORMCONFORMING ESSENTIALLY TO THE ULTIMATE EXTENSIVE CONFIGURATION OF THESTRUCTURE, COMPRISING THE STEPS OF PROVIDING A LAMINATED INFLATABLEMEMBER HAVING AN INNER LAYER CAPABLE OF RECEIVING AND RETAINING WETCEMENTITIOUS MATERIAL, LINING SAID INFLATABLE MEMBER WITH A NETWORK OFWIRE ROPES IN PREDETERMINED DESIGN, SECURING SAID LINED MEMBER TO ASUITABLE FOUNDATION, INFLATING SAID MEMBER WITH A PRESSURE GREATER THANTHE CORRESPONDING WEIGHT OF WET CEMENTITIOUS MATERIAL TO BE APPLIEDTHERETO AND THEREBY STRESSING SAID WIRE ROPES, APPLYING WET CEMENTITIOUSMATERIAL TO THE INNER SURFACE OF SAID MEMBER AND TO THE SAID WIRE ROPES,AND MAINTAINING SAID INFLATION PRESSURE WHILE THE SAID CEMENTITIOUSMATERIAL HARDENS WHEREBY THE STRESSED WIRE ROPES ARE EMBEDDED IN SAIDMATERIAL AND THE HARDENED MATERIAL IS COMPRESSED WHEN INFLATION PRESSUREIS RELEASED.